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Full text of "Text Book Of Mechanical Engineering"

Appendix VI.

1061

The resulting slag is a useful bye-product, being taken to
emery mills and ground into powder; and various important
alloys required in steel manufacture are produced by the heat
of thermit, as—

Chromium ingot
Manganese   „
Ferro-Titanium
Ferro-Boron ...
Chromium-Manganese
Manganese - Titanium
Manganese-Copper ...
Manganese-Zinc
Manganese-Tin
Nickel-Thermit

98 to 99% pure
98 to 99%    „
20 to 25 T.
25% B
30 Cr : 70 Mn

35% T
30% Mn
20% Mn
50% Mn

free from carbon

iron
lead

Pp. 339 and 832. The Water-tube Boiler. — Dealing
with the marine type of ' forcing' or quick-steaming boiler, 'where
two mud drums are connected by sets of tubes to a steam receiver
so as to form the letter A : the Yarrow and Thornycroft boilers
have already been mentioned as examples. The former is pro-
vided with perfectly straight tubes, and there is no downcomer,
some of the tubes themselves being intended to serve that pur-
pose. The Thornycroft boiler has tubes curved to meet the
draft normally, with the object of increasing the circulating effi-
ciency, and curved tubes have been adopted by many other
makers for similar reasons, not necessarily normal to draft, but
always, it is believed, having a good effect on the circulation.
The objections to these are the difficulty of internal cleaning, and
the fact that several different forms often occur in one boiler.
The White and Forster boiler, Fig. 948, is designed to overcome
the objections to curved tubes while retaining their advantages.
Referring to the figure, the stearn drum A is connected to the
mud doors B B by the tubes c c, which are all curved to the same
radius, and may be all easily withdrawn through the manhole E as
indicated by dotted lines at P. Also the interior of the tubes can
be cleaned by one curved brush G. The whole boiler is placed
within the outer casing H H, and the air for the fire enters by the
flap doors or dampers jj, thence down the passage L, being